Membrane separation, a new separation technique which emerged in the early 20th century and has rapidly developed since the 1960s, refers to a technique in which selective separation is effected when a mixture of molecules of different particle sizes passes through a semi-permeable membrane at the molecular level. The semi-permeable membrane is also referred to as a separation membrane or filtration membrane, full of pores in a membrane wall, and according to the pore sizes, can be categorized into: a microfiltration (MF) membrane, an ultrafiltration (UF) membrane, a nanofiltration (NF) membrane, a reverse osmosis (RO) membrane, etc., which all use the cross-flow filtration for membrane separation. Due to its functions of separation, concentration, purification, and refinement and its characteristics of high efficiency, energy efficiency, environmental friendliness, molecular-level filtration, simple filtration process, and easy control, the membrane separation technique has been widely used in the fields of, such as, foods, medicines, biology, environmental protection, chemical engineering, metallurgy, energy resources, petroleum, water treatments, electronics, and bionics, bringing substantial economic benefits and social benefits, and has become one of the most important approaches in current separation science. The membrane separation technique, including membrane materials, membrane assembly and optimization, membrane techniques, etc., of which the research and development has been continuously made, has become a hot spot for competition in the fields of high and new technologies between various nations in the world.